Fiber-coupled, high-speed, integrated, angled-dual-axis confocal scanning microscopes employing vertical cross-section scanning

• US 20030034431A1
• Filed: 07/01/2002
• Published: 02/20/2003
• Est. Priority Date: 07/28/2000
• Status: Active Grant

• Current Assignee: Optical Biopsy Technologies LLC
• Original Assignee: Optical Biopsy Technologies LLC
• Inventors: Kino, Gordon S., Mandella, Michael J., Garrett, Mark H.
• Granted Patent: US 6,713,742 B2
• Time in Patent Office: Days
• US Class Current: 250/201.3
• CPC Class Codes: G02B 21/0024 Confocal scanning microscopes (CSOMs) or confocal "macroscopes"; Accessories which are not restricted to use with CSOMs, e.g. sample holders
• CPC Class Codes: G02B 27/64 Imaging systems using optical elements for stabilisation of the lateral and angular position of the image

Abstract

This invention provides an angled-dual-axis confocal scanning microscope comprising a fiber-coupled, angled-dual-axis confocal scanning head and a vertical scanning unit. The angled-dual-axis confocal scanning head is configured such that an illumination beam and an observation beam intersect optimally at an angle θ within an object and the scanning is achieved by pivoting the illumination and observation beams using a single scanning element, thereby producing an arc-line scan. The vertical scanning unit causes the angled-dual-axis confocal scanning head to move towards or away from the object. By integrating the angled-dual-axis confocal scanning microscope of the present invention with fiber-optic components and a fiber-coupled laser, the present invention also provides an assembly of fiber-based angled-dual-axis confocal scanning systems that can be particularly powerful tools in biological and medical imaging applications, such as instruments for performing optical coherence microscopy and in vivo optical biopsies.

Claims

1. An angled-dual-axis confocal scanning system comprising an angled-dual-axis confocal scanning head, wherein said angled-dual-axis confocal scanning head comprises:

a) a first optical waveguide having first and second ends, for providing an illumination beam at said first end;

b) a second optical waveguide having first and second ends;

c) an angled-dual-axis focusing means for focusing said illumination beam to an illumination focal volume along an illumination axis within an object and for receiving an observation beam emanated from an observation focal volume along an observation axis within said object such that said observation beam is focused onto said first end of said second optical waveguide; and

d ) a bi-axial scanning mirror for producing a transverse cross-sectional scan, wherein said bi-axial scanning mirror is in optical communication with said focusing means and said object, wherein said bi-axial scanning mirror receives said illumination beam from said angled-dual-axis focusing means and directs said illumination beam to said illumination focal volume within said object, and wherein said bi-axial scanning mirror collects said observation beam emanated from said observation focal volume and passes said observation beam to said angled-dual-axis focusing means;

wherein said illumination axis and said observation axis intersect at an angle within said object, such that said illumination focal volume and said observation focal volume intersect at a confocal overlapping volume, and wherein said bi-axial scanning mirror is capable of pivoting said illumination and observation beams in two orthogonal directions in such a way that said illumination axis and said observation axis remain intersecting at said angle and that said confocal overlapping volume moves along a transverse cross-section within said object, thereby producing said transverse cross-sectional scan.

2. The angled-dual-axis confocal scanning system of claim 1 further comprising a vertical scanning unit, wherein said vertical scanning unit comprises:

a) a translation means mechanically coupled to said angled-dual-axis confocal scanning head; and

b) a compensation means for ensuring said intersection of said illumination focal volume and observation focal volume;

wherein said translation means is capable of causing said angled-dual-axis confocal scanning head to move relative to said object, providing a transverse cross-sectional scan at a selectable depth within said object.

3. The angled-dual-axis confocal scanning system of claim 2 wherein said compensation means comprises a fluid filling a space between said bi-axial scanning mirror and said object, wherein said fluid is substantially transparent to said illumination beam and said observation beam, and wherein said fluid has an index of refraction that is substantially the same as an index of refraction of said object.

4. The angled-dual-axis confocal scanning system of claim 3 further comprising a window means interposed between said bi-axial scanning mirror and said fluid for passage of said illumination and observation beams.

5. The angled-dual-axis confocal scanning system of claim 4 wherein said window means comprises an index matching transparent flat window adjacent to said object, wherein said window has an index of refraction that is substantially the same as an index of refraction of said object.

6. The angled-dual-axis confocal scanning system of claim 4 wherein said window means comprises a single angle-matching window element having first and second window faces in an angled arrangement, such that said illumination axis is perpendicular to said first window face and said observation axis is perpendicular to said second window face, thereby minimizing optical aberrations of said illumination and observation beams.

7. The angled-dual-axis confocal scanning system of claim 6 wherein said window element is an optical prism comprising said first and second angled window faces, and wherein said prism has an index of refraction substantially matched to said fluid.

8. The angled-dual-axis confocal scanning system of claim 3 wherein said fluid is contained in a sealed hydraulic system, including a reservoir for replenishing and receiving excess fluid in the course of vertical scans.

9. The angled-dual-axis confocal scanning system of claim 1 wherein said angled-dual-axis focusing means comprises one or more elements selected from the group consisting of refractive lenses, diffractive lenses, GRIN lenses, focusing gratings, micro-lenses, holographic optical elements, curved mirrors, and binary lenses.

10. The angled-dual-axis confocal scanning system of claim 9 wherein said angled-dual-axis focusing means comprises a single element, where said element provides said illumination axis and said observation axis.

11. The angled-dual-axis confocal scanning system of claim 9 wherein said angled-dual-axis focusing means comprises an illumination focusing element and an observation focusing element, wherein said illumination focusing element provides said illumination axis, and wherein said observation focusing element provides said observation axis.

12. The angled-dual-axis confocal scanning system of claim 11 wherein said illumination focusing element and said observation focusing element are of the same type, comprising a focusing element selected from the group consisting of refractive lenses, diffractive lenses, GRIN lenses, micro-lenses, binary lenses, and curved mirrors.

13. The angled-dual-axis confocal scanning system of claim 12 wherein said focusing element has a numerical aperture (NA) in the range of 0.1 and 0.4.

14. The angled-dual-axis confocal scanning system of claim 11 further comprising a first collimating lens, wherein said first collimating lens receives said illumination beam from said first end of said first optical waveguide and passes a collimated illumination beam to said illumination focusing element.

15. The angled-dual-axis confocal scanning system of claim 14 further comprising a second collimating lens, wherein said second collimating lens receives said observation beam from said observation focusing element and focuses said observation beam to said first end of said second optical waveguide.

16. The angled-dual-axis confocal scanning system of claim 1 wherein said bi-axial scanning mirror comprises one or more elements selected from the group consisting of silicon scanning mirrors, fast steering mirrors, flexure-type scanning mirrors, and Micro-Electro-Mechanical-Systems (MEMS) scanning micro-mirrors.

17. The angled-dual-axis confocal scanning system of claim 16 wherein said bi-axial scanning mirror comprises a single scanning mirror, wherein said scanning mirror is flat and can be pivoted about two orthogonal axes.

18. The angled-dual-axis confocal scanning system of claim 17 wherein said scanning mirror is a silicon micro-machined bi-axial scanning mirror.

19. The angled-dual-axis confocal scanning system of claim 16 wherein said bi-axial scanning mirror comprises a gimbaled assembly comprising a scanning mirror and a frame, wherein said assembly is configured such that said scanning mirror can rotate relative to said frame about a first pivoting axis and said frame along with said scanning mirror can rotate about a second pivoting axis, thereby providing rotation of said mirror in two orthogonal directions.

20. The angled-dual-axis confocal scanning system of claim 19 wherein said scanning mirror is a silicon micro-machined scanning mirror.

21. The angled-dual-axis confocal scanning system of claim 1 wherein said angled-dual-axis confocal scanning head is mechanically coupled to a substrate.

22. The angled-dual-axis confocal scanning system of claim 21 wherein said substrate comprises a silicon substrate etched with V-grooves.

23. The angled-dual-axis confocal scanning system of claim 1 wherein either of said first and second optical waveguides comprises an element selected from the group consisting of single-mode waveguides, polarization maintaining waveguides, multi-mode waveguides, birefringent waveguides, single-mode fibers, multi-mode fibers, and polarization maintaining fibers.

24. The angled-dual-axis confocal scanning system of claim 23 wherein each of said first and second optical waveguides comprises a single-mode optical fiber.

25. The angled-dual-axis confocal scanning system of claim 23 wherein said second optical waveguide is a multi-mode waveguide, whereby said observation beam is focused onto said first end of said multi-mode optical waveguide, whereby said observation beam is transmitted into said multimode waveguide.

26. The angled-dual-axis confocal scanning system of claim 25 wherein said first end of said multimode waveguide comprises a slit aperture for selecting a portion of said observation beam such that said portion is first transmitted through said slit aperture before being transmitted into said multi-mode waveguide for detection at said second end of said multi-mode waveguide.

27. The angled-dual-axis confocal scanning system of claim 1 wherein said observation beam comprises reflected light emanated from said confocal overlapping volume within said object.

28. The angled-dual-axis confocal scanning system of claim 1 wherein said observation beam comprises fluorescent light emanated from said confocal overlapping volume within said object.

29. The angled-dual-axis confocal scanning system of claim 1 wherein said illumination focal volume and said observation focal volume are diffraction-limited, determined by main lobes of said illumination beam'"'"'s point-spread function and said observation beam'"'"'s point-spread function.

30. The angled-dual-axis confocal scanning system of claim 29 wherein said confocal overlapping volume is diffraction-limited.

31. The angled-dual-axis confocal scanning system of claim 26 wherein said multi-mode waveguide is a multi-mode optical fiber.

32. The angled-dual-axis confocal scanning system of claim 1 further comprising a light source optically coupled to said second end of said first optical waveguide.

33. The angled-dual-axis confocal scanning system of claim 32 wherein said light source comprises an element selected from the group consisting of optical fiber amplifiers, fiber lasers, semiconductor optical amplifiers, semiconductor lasers, and diode-pumped solid state lasers.

34. The angled-dual-axis confocal scanning system of claim 32 wherein said light source comprises a polarized light source, and wherein said second end of said second optical waveguide is optically coupled to a polarizing beamsplitter.

35. The angled-dual-axis confocal scanning system of claim 34 further comprising two optical detectors, optically coupled to said polarizing beamsplitter.

36. The angled-dual-axis confocal scanning system of claim 1 further comprising one or more optical detectors optically coupled to said second end of said second optical waveguide.

37. The angled-dual-axis confocal scanning system of claim 36 wherein said one or more optical detectors comprise one or more elements selected from the group consisting of PIN diodes, avalanche photo diodes, and photomultiplier tube detectors.

38. A method of performing angled-dual-axis confocal scanning on a sample, comprising:

a) transmitting an illumination beam emerging from a first end of a first optical waveguide to an angled-dual-axis focusing means;

b) passing said illumination beam from said angled-dual-axis focusing means to a bi-axial scanning mirror;

c) using said bi-axial scanning mirror to direct said illumination beam to an illumination focal volume along an illumination axis within said sample;

d) using said bi-axial scanning mirror to collect an observation beam emanated from an observation focal volume along an observation axis within said sample, wherein said illumination axis and said observation axis intersect at an angle within said sample, such that said illumination focal volume and said observation focal volume intersect at a confocal overlapping volume;

e) passing said observation beam from said bi-axial scanning mirror to said angled-dual-axis focusing means;

f) focusing said observation beam to a first end of a second optical waveguide; and

g) pivoting said bi-axial scanning mirror in such a way that said illumination axis and said observation axis remain intersecting at said angle and that said confocal overlapping volume moves along a transverse cross-section within said sample, thereby producing a transverse cross-sectional scan.

39. The method of claim 38 further comprising the step of moving said first ends of said first and second optical waveguides, said angled-dual-axis focusing means, and said bi-axial scanning mirror in unity relative to said sample and repeating said step of g), whereby a succession of transverse cross-sectional scans that progressively deepen into said sample is produced, thereby providing transverse cross-sectional scans at varying depths within said sample.

40. The method of claim 39 further comprising the step of filling a space between said bi-axial scanning mirror and said sample with a fluid, wherein said fluid is substantially transparent to said illumination beam and said observation beam, and wherein said fluid has an index of refraction that is substantially the same as an index of refraction of said sample, for ensuring said intersection of said illumination focal volume and said observation focal volume in the course of varying the depth at which transverse cross-sectional scans are produced.

41. The method of claim 40 further comprising the step of disposing a window means between said bi-axial scanning mirror and said fluid for passage of said illumination and observation beams.

42. The method of claim 40 further comprising the step of disposing a transparent window between said fluid and said sample for passage of said illumination and observation beams.

43. The method of claim 38 further comprising the step of mechanically coupling said first ends of said first and second waveguides, said angled-dual-axis focusing means, and said bi-axial scanning mirror to a substrate.

44. The method of claim 38 wherein said bi-axial scanning mirror comprises a flat scanning mirror that can be pivoted about two orthogonal axes.

45. The method of claim 44 wherein said bi-axial scanning mirror is a silicon micro-machined scanning mirror.

46. The method of claim 38 wherein said first optical waveguide is a single-mode waveguide, whereby said first end of said single-mode waveguide provides a point source of light, thereby providing said illumination beam.

47. The method of claim 38 wherein said second optical waveguide is a multi-mode waveguide.

48. The method of claim 47 wherein said first end of said multimode waveguide comprises a slit aperture for selecting a portion of said observation beam such that said portion is first transmitted through said slit aperture before being transmitted into said multi-mode waveguide.

49. The method of claim 48 wherein said slit aperture is a slit mask formed onto said first end of said multimode waveguide.

50. The method of claim 38 wherein said angled-dual-axis focusing means comprises a single element, wherein said element provides said illumination axis and said observation axis.

51. The method of claim 38 wherein said angled-dual-axis focusing means comprises an illumination focusing element and an observation focusing element, wherein said illumination focusing element provides said illumination axis, and wherein said observation focusing element provides said observation axis.

52. The method of claim 38 further comprising the step of coupling a second end of said first optical waveguide to a light source and a second end of said second optical waveguide to an optical detector, such that said illumination beam is transmitted from said light source and said observation beam is routed to said optical detector.